The present invention relates to a racket used in sport events such as tennis, badminton, and squash (or formally a squash racquets), and more particularly to a racket capable of striking strong balls by an increased moment of inertia effectuated by moving the center of gravity in the direction of racket head (or racket tip) at the time of the swing.
There have been various inventions disclosed conventionally for rackets which are capable of shifting their center of gravities in the direction of the racket heads. Such inventions include rackets disclosed in JP-A (Japanese Patent Application Laid-Open) No. 63-318966, 64-40071, and JP-U (Japanese Utility Model Application Laid-Open) No. 04-870, and 04-27953.
For instance, JP-A 63-318966 discloses a racket which disposes narrow tubes or narrow holes along the stringing frame and the neck portion, within which a moving body is inserted in a state to move around freely. At the time of swinging the racket strongly, the moving body moves in the direction of the racket head by centrifugal force caused by the swing, and moves the point (or location) of the center of gravity of the racket towards the racket head.
According to this invention, a racket capable of shifting its center of gravity to strike back strong balls feels relatively light at the beginning of the swing, changes to top heavy, utilizing a principle of pendulum.
JP-A 64-40071 teaches a racket comprising a frame defining an outer portion of the hitting surface, a grip connected to the frame, stringing provided within an outer hull defined by the frame to configure a hitting surface, wherein a balancer capable of moving freely between a position closer to the grip and a position opposite which is closer to the racket head, is provided at the frame, and an urging means to constantly urge the balancer to the position closer to the grip.
JP-U 4-27953 demonstrates a tennis racket which forms a frame and a grip as one continuous pipe wherein a fluid body such as water is filled within the pipe leaving out some spaces.
According to this tennis racket, when a player swings the racket horizontally, the centrifugal force carries the water within the pipe in the direction of the racket tip, making the racket in a state of top heavy. On the other hand, when the racket is stood up vertically as in the case of hitting volleys, the water remains around the grip, leaving the racket tip relatively lighter, thus lightens the swing itself.
However, by using the racket disclosed in JP-A 63-318966, there is a risk of destroying the cylinder body by accidental contact with a ball, when cylinder body enclosing a balancer is disposed along the inner circumference of the face portion of the racket frame. Also, because the cylinder body restrains the motion of the stringing (i.e., interferes with the stringing) provided within the inner circumference of the face portion, there is a risk of losing rebounding force of the ball being hit by the racket. On the other hand, when the cylinder body is disposed on the outer circumference of the face portion of the frame, there is a risk of damaging the cylinder body by accidental impact with the ground in an attempt to strike back low balls, or disturbs the swing, which leads to inferior maneuverability of the racket.
The racket disclosed in the aforementioned JP-A 64-40071 may have a problem of damaging the racket during the play, which attributes to disposition of the balancer in the frame, as with the racket of JP-A 63-318966.
A racket disclosed in JP-U 4-27953 may exhibit uncomfortable feeling of use during the swing when tapping noise of the water injected in the pipe caused by leaving out some air spaces within the pipe moves inside the frame, leading to plurality of water surfaces existing in the pipe. The racket may be slow in shifting the center of gravity since the air within the pipe may be divided into some air lumps which moves in opposite direction to the water, and since the difference of the specific gravity of water and that of the air is as small as 1, when the centrifugal force is exerted to the water and the air, the lumps of air moves slowly, and leads to decreased moving speed of the center of gravity. Further, when the racket is rapidly shaken, air lumps are decoupled in many minute air bubbles, and since the moving resistance of the bubble in water is extremely large, causes the motion of the bubbles to slow down, which generates slow movement in the center of gravity when the racket is shaken.
Under such circumstances, an object of the present invention is to overcome aforementioned problems, and to achieve a goal described hereinafter. The object of the present invention is to provide a racket, specifically a tennis racket devised to striking back strong balls by an increased moment of inertia, which demonstrates a smooth shift in the center of gravity of the racket during the swing.
A racket comprising a frame body having a face portion, a shaft portion, and a grip portion, wherein grooves, which are the length of 10% to 20% of the entire circumference of the face portion of the frame body, are provided at two maximum width points of the face portion. A closed tube enclosing a slidable weight weighing 2 g to 10 g is disposed in the groove.
According to the present invention, the racket is used for use in badminton, squash, or preferably tennis and is capable of striking strong balls, and demonstrating outstanding increase in the moment of inertia is provided which comprises a groove adjusted in the shape and length of a tube which encloses a lead of predetermined length, provided in two portions covering the points of maximum width of a frame comprising a face portion. By embedding the tube in the groove so that the outer surface of the tube does not exceed the outer surface of the frame, or in other words, the tube is disposed in the groove so that it does not protrude from the surface of the frame. The present invention allows the lead to smoothly slide in the direction of the racket tip when the centrifugal force is exerted to the racket, and to smoothly slide downward in the direction of the grip by the force of gravity when the racket is stood upwards.